1. Field of Invention
This invention relates to internal combustion engines and more specifically to engines of increased volumetric efficiency, simplified construction and reduced emissions.
2. Prior Art
Presently, automotive and other internal combustion engine design is being influenced by average fuel economy legislation, emission control legislation or both. These complex and often contradictory initiatives have forced manufacturers to mass produce more sophisticated internal combustion engines. This has driven up the cost of manufacture and increased complexity.
An important part in current engine development is played by the computer. Embedded controllers and their sensors and controlled outputs allow a complexity of engine management not possible in other known manner. An important developmental field of engine management related to emissions and power output is variable valve timing. That is, a computer, reacting to sensor input and a prepared software program directly controls opening and closing of an engine valve. This allows the opening amount [lift] and the opening time [duration] as well as the relationship between these events [centerline and overlap] for each valve to be controlled individually and variably. It also becomes possible to selectively not open a valve at all; for example, to assist vehicle braking or reduce part throttle pumping losses by using less than the maximum number of engine cylinders at a given moment.
While the advantages of computer engine management in general and computer management of engine valves in particular are well known in the art it has not been possible to date to conceive and manufacture a working, reliable and simple poppet valve controller. This is essentially because the electrical or other power requirements to do this work are relatively large and become even larger as engine crankshaft speed increases. Another problem is the impact loads developed, especially during valve closing. This problem also worsens as engine speed increases. While a poppet valve must rapidly accelerate to a high speed at the beginning of travel, it must complete this travel at a relatively low speed if the valve and its engine are to have a suitably long life and low noise and vibration.
The use of sleeve valves in piston engines of all types is well known in the art. Double and then later single sleeve valves were widely used in the 1920 to 1940s era in automotive, heavy duty gasoline, diesel and aircraft piston engines. Design improvements culminated in several high performance military air and liquid cooled aircraft powerplants used in the world war two period. Developers and Manufacturers included, for example Pratt and Whitney, Continental Engines, Napiers, Bristol Aircraft and Rolls-Royce.
These engines used a single sleeve valve in combination with a re-entrant or junk head. This type of head and sleeve combination utilizes sealing rings in the cylinder head and upper sleeve area. Intake and exhaust ports are pierced through the sleeve walls and depend on both reciprocation and partial rotation of the sleeve for timed alignment with appropriate port openings in the engine cylinder block to accomplish intake and exhaust processes. Although both high specific power outputs and long service life were achieved with various makes and models of these engines the rapid development of gas turbine aircraft engines in 1945 and later signaled the end of high output aircraft piston engine development in the world. Also eclipsed by the development of aircraft gas turbines was the later, simplified and superior sleeve development developed by Harry Ricardo. This sleeve differed from the above described junk head, pierced sleeve design by being a simple cylindrical shape with sealing accomplished by heat expansion of the sleeve periphery to the cylinder head. Because this sleeve is not pierced for exhaust ports, but simply allows this function to be performed over the top edge of the cylindrical sleeve, engine operation is greatly simplified at the same time as the effective valve area is greatly increased.
This sleeve valve design is described in U.S. Pat. No. 2,318,333 and also in a book by Harry Ricardo, "The High Speed Internal Combustion Engine" 4th edition and 5th edition.
Said book describes a later, improved version of the sleeve design detailed in U.S. Pat. No. 2,318,833 and gives a fuller explanation of the sealing function. The described engine is a developmental, single cylinder version of what became a Rolls-Royce production military aircraft engine, the Crecy, also referred to as the P.I. 26 [Petrol Injection, 26 liter displacement]. This engine is briefly described in the above noted book as well as "Rolls-Royce and the Mustang" by David Birch, Rolls-Royce Heritage Trust [1987].
These engines were two-cycle, highly supercharged stratified charge direct injection gasoline engines. The single-cylinder, 100 cubic inch developmental engines ultimately produced over 350 horsepower on 100 octane fuel. The use of this sleeve design as an exhaust valve in such a highly supercharged, two-stroke engine serves to demonstrate its robust nature and ability to seal reliably under very high temperatures and speeds.
However, a limiting feature of this engine and sleeve design is that it can be used with a two-stroke engine design only. This uniflow scavenged engine had intake air forced through slots in the sleeve lower end after the descending piston uncovered said slots. This air forced exhaust gases out the open sleeve exhaust valve until either the rising piston or valve closure stopped the flow in a manner similar to some two-cycle production diesel engines.